This invention relates in general to semiconductor devices and in particular relates to a package for thyristors of the type used in power circuits.
Thyristors are employed for various purposes in electrical power and control circuits. An example is the use of thyristors as high voltage distribution equipment. In such applications control problems arise due to factors such as noise signal pickup, also, high voltage potentials across the control leads used to trigger the thyristors must be avoided by expensive means such as individual transformers.
It would be desirable to employ a light-triggered thyristor in power circuits of the foregoing nature so as to isolate the control signal from the power signal and thereby eliminate noise pickup and control problems. However, it has heretofore not been feasible to employ light-triggered thyristors in power circuits because of the necessity for hermetically sealing such thyristors. The pole faces of power semiconductor devices require massive thermal and electrical contact to handle the relatively large currents, and it has not been feasible to introduce a triggering light signal to a light-sensitive region of one of these pole faces while maintaining hermeticity of the package. There is further the requirement of providing a suitable external connection between the package and the light source, such as a fiber optic cable. Previously the differences in coefficients of thermal expansion between glass light pipes and other elements of the package have precluded a practical hermetically sealed thyristor package for power circuits.